Qn the Temperature of Fishes. 827 



The respiratory nerves of the other species of thynnus which 

 I have examined, very much resemble the preceding. Those 

 which are smallest belong to Thynnus brevipinnis, and yet, even 

 in this fish, in comparison with the fish of other tribes, the re- 

 spiratory nerves are large, and their ganglia considerable. This 

 fish, perhaps, may be considered as a link between the tunny 

 family and the mackerel on one side, and the pelamides on the 

 other ; and the respiratory nerves of one of each of those genera 

 of fish, which I have dissected, viz., of Scomber pneumatopho- 

 rus and Pelamys sarda, have approached in magnitude those of 

 the thynnus last mentioned. What the temperature of those 

 fish is, I have not had an opportunity of determining by trial ; 

 according to the statement of the fishermen I have consulted, 

 they are all cold-blooded. Reasoning from analogy, the natu- 

 ral inference is, that they will be found to be of somewhat high- 

 er temperature than other fishes less amply supplied with respi- 

 ratory nerves. 



As regards the rationale of the high temperature of the thyn- 

 ni, there appears to me less difficulty, than in accounting for the 

 electrical power exercised by the torpedo, and other electrical 

 fish. The peculiar function of the latter is performed by means 

 of a particular organ, the most striking feature of which is a vast 

 apparatus of nerves ; but this organization bears little or no ana- 

 logy to any other natural, or to any artificial process hitherto 

 known, by which electricity is generated. Not so the respiratory 

 apparatus, and associated organs in these fish of high tempera- 

 ture ; they are essentially analogous in organization to the warm- 

 blooded animals of the other two classes, and hardly more diffe- 

 rent from those of the mammalia, than those of the mammalia 

 are from the respiratory apparatus and associated organs of 

 birds. The function of respiration in water is commonly con- 

 sidered the same as in the atmosphere ; the same change, it is 

 supposed, takes place in the blood ; the same change is ascer- 

 tained to take place in the air dissolved ; and, increase of tem- 

 perature in one instance and the other, is referred to the con- 

 version of carbon into carbonic acid. The difficulty is not as 

 regards the kind of effect, but the degree of that effect ; not an 

 augmentation of c-ne or two degrees above the temperature of 

 the surrounding medium, but of many degrees. The considera. 



